The present invention relates to an encoder and a decoder for an information transmission system that operative to insert obtain an identification number or the like into from a video signal without affecting the video signal. The identification number is used to identify a video source produced in a broadcasting station. Moreover, the present invention relates to an encoder and the decoder for the informant on transmission system that can identify precisely where the information signal is to be inserted into the video signal even if the video signal is a moving image signal.
It is important to apply an identification number or a special information of producer to a video source. Thus, an original video source (broadcasting program or the like) produced by a broadcasting station or the like can be distinguished from another video source so that the producer can assert its copyrights.
It may be considered desirable to: insert character information, such as characters, marks or the like, as well as the identification information dispersively into the video signal; store the character information of such characters and marks in a receiver; and rearrange characters, marks or the like. Thus, the characters, marks or the like can be used as useful information.
In order to add the identification information such as video source to the video signal or insert the character information dispersively into the video signal, these information signals may be inserted into a vertical blanking interval of the video signal. Moreover, the information signal may be superimposed outside of an effective screen area of the video signal.
It is desirable that the superimposed information signal does not adversely affect the video signal and that it cannot be easily modified.
When the information signal is inserted into the vertical blanking interval of the video signal, it is relatively easy to scan the blanking interval and analyze which kind of information is inserted or which line is used to insert the information. Thus, it may be important to encode the information to prevent it from being analyzed. If a third party can analyze which horizontal line is used to insert the information signal, there may be a possibility of exchanging the inserted information with new information.
Assuming the information signal is inserted into a portion of the video signal representative of a region outside of the effective screen area, an image of the information signal inserted into the video signal may appear on the screen regardless of the contents of the image. This information appearance depends on the definition of the effective screen area.
If the information signal is inserted into a portion of the video signal representative of a region inside of the effective screen area, there may be a large problem that the information signal interferes with the original image. In other words, when the information signal is inserted strongly, it may be easy to detect it but the interference with the original image may become noticeable. When the information signal is inserted faintly, the interference may be improved but it is difficult to detect the information signal.
What is desired is an encoder/decoder for an information signal that overcomes the aforementioned disadvantages. The encoder/decoder should keep the information secret, and the contents of the information should be difficult to be modified. The encoder/decoder should maintain the information when using a recording apparatus, such as a VTR. In addition, the encoder/decoder should be simple in construction.